Costco’s $4.43B Surge to 13th in Volume Can’t Offset 2.9% Drop as Investors Await Earnings

On September 26, 2025, Costco (COST) recorded a trading volume of $4.43 billion, marking a 57.38% increase from the previous day’s activity and securing the 13th highest volume among listed stocks. Despite the surge in liquidity, shares closed down 2.90%, reflecting investor caution ahead of upcoming earnings and macroeconomic data releases.

Recent market activity suggests heightened sensitivity to consumer sentiment metrics and supply chain dynamics. Analysts noted that Costco’s performance aligns with broader retail sector volatility, as investors recalibrate expectations for holiday season demand. The company’s recent pricing strategies and membership growth metrics remain under scrutiny, though no new earnings reports or corporate announcements have triggered immediate directional bias in the stock.

To execute this back-test accurately, constructing a daily-rebalanced, 500-stock, equal-weight portfolio is necessary—effectively a multi-asset strategy. The current back-test engine is optimized for single-ticker or single-event evaluations, meaning a fully automated simulation of a "top-500-by-volume" portfolio is not directly supported. A representative proxy, such as comparing the SPY ETF against a high-liquidity counterpart like RSP, could serve as an alternative approach. Confirmation on market universe parameters, ranking metrics, and weighting methodology is required to finalize the study design.